Abstract: In order to improve the mechanical properties of large-tonnage elevator car frame and further reduce the weight of the car frame structure, a parametric car frame model is established by Ansys Workbench. The static load & dynamic load analysis and modal analysis are carried out. The topology optimization model of the bridge bottom frame and pull rod is established with variable-density method. Based on the topology optimization results, the structure layout of the original bridge bottom frame and pull rod is reconstructed. Then, taking the minimum total mass of the car frame structure as the optimization objective and the value range of the standard parameters of the component and the maximum deformation value of the bridge as the constraint conditions, the size optimization model of the bridge frame is constructed. In order to improve the solving speed, a discrete parameter fitting design method is proposed for the steel cross-section, the parameters of the car frame are related to the assembly size and the selection design is proposed according to the parameter fitting. The parameter selection after optimization is completed. The results show that the optimized car frame structure can meet the design requirements of lightweight, safety requirement and the mechanical properties.